<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<style>
  .triangle{
    width: 0px;
    height: 0px;
    border-top: 30px solid pink;
    border-bottom: 30px solid transparent;
    border-left: 30px solid transparent;
    border-right: 30px solid transparent;
  }
</style>
<body>
  <div class="triangle"></div>
</body>
</html>